Apparatus for treating a gas formed from a waste in a molten metal bath

ABSTRACT

A method and a system is disclosed for treating a gaseous discharge stream formed from a waste in a molten metal bath. The waste is directed into a reactor containing a molten metal bath. The molten metal bath has operating conditions which are sufficient to dissociate the waste and form a gaseous discharge stream including a dissociation product. The gaseous discharge stream is cooled in a cooling section and the dissociation product is separated, as a particulate, from a gaseous component of the gaseous discharge stream. The fluid particulate stream is recirculated to the gaseous discharge stream in a reaction section of the apparatus.

This application is a division of application Ser. No. 08/041,491 filedApr. 1, 1993, now U.S. Pat. No. 5,585,532 which is acontinuation-in-part of 08/023,696, filed Feb. 26, 1993, now U.S. Pat.No. 5,358,697 which is a divisional of 737,048, filed Jul. 29, 1991,U.S. Pat. No. 5,191,154, issued Mar. 2, 1993.

BACKGROUND OF THE INVENTION

The Environmental Protection Agency (EPA) has estimated that the annualgeneration of hazardous wastes is in excess of seventy billion gallons.Hazardous wastes include organic materials, such as polychlorinatedbiphenyls, pesticides, herbicides, municipal garbage, hospital wastesincluding pathogens, paints, inks and contaminated solvents, blackliquor and explosives. Examples of inorganic wastes include oxides ofiron, zinc, copper, lead, magnesium, aluminum, chromium and cadmium,various powdered metal manufacturing residues and metal-containingsludges.

Further, the EPA has classified as toxic, ignitable, corrosive ordangerously reactive many common waste materials, such as paint sludgefrom appliance factories, dregs of chrome and nickel from metal platingshops, spent raw materials for varnish, carpets and detergents atchemical plants, solvents from dry-cleaned clothes and degreasedmicrochips from computers, mercury from exhausted watch batteries,butane residue from disposable cigarette lighters and lye from cans ofoven cleaners.

Landfills are becoming less available as a means of disposing of suchwastes. In the absence of suitable landfills, hazardous wastes must betransformed to benign and, preferably, useful development of alternativemethods of treating hazardous wastes. Various types of reactors whichhave been employed for decomposition of hazardous wastes include, forexample, liquid injection, multiple hearth, multiple chamber, fluidizedbed, molten salt and high efficiency-type boiler reactors. However, manyreactors release gases which must be contained or destroyed. Often,these gases are burned, which generally causes formation of freeradicals because of the short residence time of the off-gases at flametemperature.

Rotary kilns are a commonly-used type of reactor for combustion oforganic wastes. Combustion in rotary kilns typically is initiated by ahigh temperature flame, whereby reactive species are generated from theorganic wastes and then oxidized. However, it is often difficult tocontact reactive species with oxygen for oxidation because of poormixing within the rotary kilns. The rate of destruction of the waste,therefore, can be impeded. Moreover, heat released by combustion occursaway from the flame tip as reacting materials are fed through the rotarykiln, thereby limiting the heat which can be utilized for the initialstep of generating reactive species.

Titus, et al., U.S. Pat. No. 3,812,620, disclose a molten pool of glassand miscellaneous metals formed during incineration of "heterogenouswaste materials," such as municipal garbage. Various organics in thewaste materials are decomposed in the molten pool at temperatures of upto 10,000° F. However, the decomposed materials often are not contactedwith oxygen introduced into the molten pool.

Molten salt processes are also known, and are typified by theconsumption of solvents and salts in a caustic molten bath into whichoxygen and wastes are injected. However, such baths are generallylimited to degradation of wastes by chemical reaction rather thanthermal destruction. See, for example, U.S. Pat. Nos. 4,447,262,4,246,255 and 4,017,271.

Oxidation of wastes by reaction of organic materials and oxygen in thepresence of water at high temperature and pressure is another method ofdisposal. See, Wilhelmi, A. R. et al., Chem. Eng. Prog., 75:46-52(1979). However, inorganic salts, char and metal-containing solids canaccumulate at the walls of apparatus employed for such methods, thusnecessitating removal of accumulated deposits, causing corrosion andlimiting the operating capacity and useful life of such apparatus.

SUMMARY OF THE INVENTION

The present invention relates to a new method and apparatus for treatinga gaseous discharge stream formed from a waste in a molten metal bath.

The method includes directing the waste into a molten metal bath withinthe reactor. The molten metal bath has operating conditions which aresufficient to dissociate the waste and to form a gaseous dischargestream including a dissociation product. The gaseous discharge stream iscooled and the dissociation product is separated as a particulate from agaseous component of the gaseous discharge stream, thereby forming aparticulate stream. At least a portion of the particulate stream isrecirculated to the gaseous discharge stream.

The apparatus includes a reactor, having a molten metal bath formedtherein, and a gaseous discharge portion above the molten metal bath. Areaction section extends from the gaseous discharge port. A coolingcolumn extends from the reaction section. Separation means are in fluidcommunication with the cooling section for separating the particulatedissociation product from a gaseous component of a gaseous dischargestream formed from a waste in the reactor, and passing from the reactorthrough the reaction section and the cooling column into the separationmeans. A gaseous discharge conduit extends from the separation means. Acooling section extends from the separation means for cooling aparticulate stream formed of the particulate dissociation product whichhas been separated from the gaseous discharge stream in the separationmeans. A recirculation conduit extends from the cooling section to thereaction section for conducting at least a portion of the particulatestream from the cooling section to the reaction section.

This invention has many advantages. Chemical reaction of the wastecauses formation of intermediate components, such as light hydrocarbons,and of atomic constituents. At least a portion of the atomicconstituents are reactive with other components of the molten bath, suchas oxygen, thereby allowing formation of relatively stable compounds,such as hydrogen gas and carbon monoxide. Heat generated by exothermicreaction of the atomic constituents can be sufficient to initiateadditional chemical reaction of waste. Relatively volatile feed can beintroduced on top of a molten metal bath for chemical reaction. Asubstantial portion of any condensable, absorbable, adsorbable orsurface-action intermediate components which volatilize and are emittedfrom the reactor with the off-gas are returned to the molten metal bathfor chemical reaction, such as conversion to atomic constituents, andsubsequent exothermic reaction of the atomic constituents to formrelatively stable compounds.

The molten metal bath can include immiscible metals, allowing selectionof combinations of metals according to relative solubility and freeenergies of oxidation, whereby reaction of reactive components can becontrolled to form relatively stable compounds. Chemical, mass andthermal energies can be transferred within the molten bath to createphysicochemical environments which can lead to formation ofthermodynamically stable compounds at the conditions specified by eachphase of a multi-phase molten bath.

The high solubility of resultant compounds in the individual phases ofthe multi-phase reaction system permits collection of significantamounts of these compounds by the respective phases. Many of thecompounds formed can be disposed of by incorporation into a vitreousnon-leachable crystallographic matrix of a vitreous layer disposed overthe molten metal. Gaseous emissions of deleterious compounds can therebybe further reduced.

Further, recirculating a cooled portion of a particulate bed formed fromthe off-gas can increase the rate of kinetically-controlled reactions,thereby suppressing dioxin formation. Also, thermodynamically-favoredreactions can be suppressed, thereby selectively enhancing the formationof such products as methane. In addition, components of the off-gas,such as fine particles and volatilized heavy metals, can be recovered.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a section view of one embodiment of the apparatus of theinvention.

FIG. 2 is a section of one embodiment of apparatus suitable for treatinga gaseous stream produced by the apparatus shown in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

The features and other details of the method of the invention will nowbe more particularly described with reference to the accompanying figureand pointed out in the claims. It will be understood that particularembodiments of the invention are shown by way of illustration and not aslimitations of the invention. The principal functions of this inventioncan be employed in various embodiments without departing from the scopeof the invention.

The present invention generally relates to a method and system forcontrolling decomposition of a feed composition in a molten metal bath.Processes for decomposing waste in molten metal baths are disclosed inU.S. Pat. Nos. 4,574,714, 4,602,574 and 5,177,304, the teachings ofwhich are hereby incorporated by reference.

In one embodiment of the invention, illustrated in FIG. 1, system 10includes reactor 12. Examples of suitable vessels include K-BOP, Q-BOP,argon-oxygen decarbonization furnace (AOD), EAF, etc., such as are knownin the art. Reactor 12 has an upper portion 14, and a lower portion 16.Feed inlet 18 at upper portion 14 of reactor 12 is suitable fordirecting feed into reactor 12. Off-gas outlet 22 extends from upperportion 14 and is suitable for conducting an off-gas out of reactor 12.

Tuyere 28 includes coolant tube 30, oxidant inlet tube 24 and feed inlettube 35. Coolant tube 30 extends from coolant source 34 to reactor 12.Oxidant inlet tube 24 extends from oxidant source 26 to lower portion 16of reactor 12. Oxidant inlet tube 24 is disposed within coolant tube 30at tuyere opening 32. Feed inlet tube 35 extends from feed source 37 totuyere 28. Feed inlet tube 35 is disposed within oxidant inlet tube 24at tuyere opening 32. Pump 39 is disposed at tuyere 28 to direct asuitable feed from feed source 37 and through tuyere opening 32 intoreactor 12. Tuyere 28 is dimensioned and configured for conjointly andcontinuously introducing a suitable carbon-containing gas and oxidantinto reactor 12.

It is to be understood, however, that the coolant and oxidant can beintroduced to reactor 12 separately and/or intermittently, rather thanconjointly and continuously. It is also to be understood that more thanone tuyere 28 can be disposed in reactor 12 and that concentric, ormultiple concentric tuyeres, can be employed for separate introductionof reactants, such as feed and oxidant, into reactor 12. For example,the feed can be introduced through a first double concentric tuyere, notshown, and the oxidant can be separately introduced through a seconddouble concentric tuyere, also not shown, as an alternative to employingtuyere 28. Double concentric tuyeres, such as for separate introductionof feed and oxidant, can be located proximately or remotely from eachother in reactor 12. Further, it is to be understood that feed can beintroduced into reactor 12 by other suitable methods, such as byemploying a consumable lance, etc. In one embodiment, the feed andoxidant are introduced according to the method and system described inU.S. Patent Application, titled "Method and System of Formation andOxidation of Dissolved Atomic Constituents in a Molten Bath" and filedby Casey E. McGeever and Christopher J. Nagel, the teachings of whichare incorporated herein by reference.

Bottom-tapping spout 36 extends from lower portion 16 and is suitablefor removal of at least a portion of a molten bath from reactor 12.Additional drains can be provided as a means of continuously orintermittently removing distinct molten phases. Material can also beremoved by other methods, such as are known in the art. For example,material can be removed from reactor 12 by rotating vessel 12 andemploying a launder, not shown, extending from feed inlet 18.Alternatively, the launder can extend into reactor 12 through a taphole, also not shown.

Induction coil 38 is disposed at lower portion 16 for heating reactor 12or for initiating generation of heat within reactor 12. It is to beunderstood that, alternatively, reactor 12 can be heated by othersuitable means, such as by oxyfuel burners, electric arc, etc. Trunions40 are disposed at reactor 12 for manipulation of reactor 12. Seal 42 isdisposed between reactor 12 and off-gas outlet 22 and is suitable forallowing partial rotation of reactor 12 about trunions 40 withoutbreaking seal 42. Alternatively, reactor 12 does not include trunions 40or seal 42 and does not rotate. Reactor 12 is constructed of suitablematerials, such as are known in the art.

Molten metal bath 44 is disposed within reactor 12. In one embodiment,molten metal bath 44 includes a metal having a free energy of oxidation,at operating conditions of system 10, which is greater than that ofconversion of atomic carbon to carbon monoxide. In one example, moltenmetal bath 44 includes carbon in an amount in the of between about 1/2percent and about six percent by weight. The amount of carbon in moltenmetal bath 44 can be controlled, for example: by introduction of a feed,which includes carbon and oxidant, to molten metal bath 44; bycontrolling the rate of removal of off-gas from molten metal bath 44; bycontrolling system conditions, e.g., temperature, of system 10; bycontrolling the relative amounts of other components in molten metalbath 44; etc.

Examples of suitable metals in molten metal bath 44 include iron,chromium, manganese, copper, nickel, cobalt, etc. It is to be understoodthat molten metal bath 44 can include more than one metal. For example,molten metal bath 44 can include a solution of metals. Also, it is to beunderstood that molten metal bath 44 can include oxides of the moltenmetals. As disclosed in U.S. patent application Ser. No. 07/557,561,molten metal bath 44 can include more than one phase of molten metal. Inone embodiment, molten metal bath 44 is formed of a vitreous phase whichincludes at least one metal oxide and does not include a molten metalphase. In another embodiment, the vitreous phase can include at leastone salt. Alternatively, a substantial portion of molten metal bath 44can be of elemental metal.

Molten metal bath 44 includes first molten metal phase 46 and secondmolten metal phase 48, which is substantially immiscible in first moltenmetal phase 46. Both first molten metal phase 46 and second molten metalphase 48 can comprise solutions of metals. The solubility of atomiccarbon in second molten metal phase 48 can be significantly less than infirst molten metal phase 46.

First molten metal phase 46 has a free energy of oxidation, at operatingconditions of system 10, greater than that of oxidation of atomic carbonto form carbon monoxide. Second molten metal phase 48 has a free energyof oxidation at the operating conditions of system 10 greater than thatof oxidation of carbon monoxide to form carbon dioxide. Oxidation ofatomic carbon, therefore, is more complete because carbon monoxide,which is formed from atomic carbon in first molten metal phase 46, issubstantially converted to carbon dioxide in second molten metal phase48.

Molten metal bath 44 can be formed by at least partially filling reactor12 with a suitable metal. The metal is then heated to a suitabletemperature by activating induction coil 38 or by other means, notshown. Where two immiscible metals are introduced to reactor 12, themetals separate during melting to form first molten metal phase 46 andsecond molten metal phase 48. In one embodiment, the viscosity of atleast one phase of molten metal bath 44 is less than about tencentipoise at the operating conditions of system 10. In anotherembodiment, the viscosity of at least one phase of molten metal bath 44is less than about thirty poise at the operating conditions of system10.

In one embodiment, suitable operating conditions of system 10 include atemperature sufficient to chemically react waste feed from feed source37 and thereby form at least one intermediate component. "Intermediatecomponent," as that term is used herein, means a component which isformed from feed and which can be chemically reacted, such as byconversion to atomic constituents, for subsequent reaction with acomponent of molten metal bath 44. The intermediate component can be,for example, an organic compound or an inorganic compound. In oneembodiment, the operating conditions of molten metal bath 44 include atemperature sufficient to cause the free energy of oxidation of metal inmolten metal bath 44 to be greater than that of conversion of atomiccarbon to carbon monoxide. The temperature of molten metal bath 44 isalso sufficient to cause molten metal bath 44 to convert carbon in theintermediate component to atomic carbon.

Vitreous layer 50 is disposed on molten metal bath 44. Vitreous layer 50is substantially immiscible with molten metal bath 44. Alternatively,system 10 does not include vitreous layer 50. Vitreous layer 50 includesat least one metal oxide, the metal element of which has a free energyof oxidation, at operating conditions of system 10, less than the freeenergy of oxidation of atomic carbon to carbon monoxide.

The solubility of carbon and of carbon monoxide in vitreous layer 50 canbe less than that of molten metal bath 44, thereby causing atomic carbonand carbon monoxide to be retained within molten metal bath 44. Inanother embodiment, vitreous layer 50 has a lower thermal conductivitythan that of molten metal bath 44. Radiant loss of heat from moltenmetal bath 44 can thereby be reduced to significantly below the radiantheat loss from molten metal bath 44 when no vitreous layer 50 ispresent.

Examples of suitable metal oxides of vitreous layer 50 include titaniumoxide (TiO₂), zirconium oxide (ZrO₂), aluminum oxide (Al₂ O₃), magnesiumoxide (MgO), calcium oxide (CaO), silica (SiO₂), etc. Other examples ofsuitable components of vitreous layer 50 include halogens, sulfur,phosphorus, heavy metals, etc. It is to be understood that vitreouslayer 50 can include more than one metal oxide. Vitreous layer 50 cancontain more than one phase. Typically, vitreous layer 50 issubstantially fluid and free radicals and other gases can pass acrossvitreous layer 50 from molten metal bath 44.

Vitreous layer 50 can be formed by directing suitable materials, such asmetals, metal oxides, halogens, sulfur, phosphorus, heavy metals,sludges, etc., from source 52 through inlet tube 54 and into moltenmetal bath 44. Inorganic components of feed 20 can also be included invitreous layer 50. The materials from source 52 can be directed onto thetop of molten metal bath 44 or injected into molten metal bath 44, usingmethods such as are well-known in the art. The materials can form otherstable compounds at the operating conditions of system 10 by reaction,for example, with alkali metal cations or alkaline earth metal cations.Examples of such stable reaction products include calcium fluoride(CaF₂) and magnesium phosphate (Mg(PO₄)₂). In one embodiment, vitreouslayer 50 contains is about forty percent calcium oxide, about fortypercent silicone dioxide and about twenty percent aluminum oxide, and isabout five inches thick.

Feed, such as a waste in solid or liquid form, is directed from feedsource 37 into reactor 12. The feed can be introduced to reactor throughline 35, line 51 and/or line 53. Generally, the feed includes organiccompounds, such as alkenes, alkanes, etc. Alternatively, the feed can bedirected into reactor 12 through inlet 18 as whole articles, such aspaper products, lumber, tires, coal, etc. It is to be understood thatinorganic compositions can also be used as feed for introduction andchemical reaction in system 10. Suitable examples of inorganic feedsinclude, but are not limited to, metals and their oxides, sulfides andhalides. In addition to carbon, feed can include other atomicconstituents, such as hydrogen, halide, metals, etc.

The feed directed into reactor 12 combines with molten metal bath 44 andcan also combine with vitreous layer 50. Contact of the feed with moltenmetal bath 44 or vitreous layer 50 exposes the feed to conditionssufficient to chemically react at least a portion of the components inthe feed. Chemical reaction of the feed causes formation of at least oneintermediate component.

The feed, oxidant and coolant are directed into molten metal bath 44through tuyere 28. The feed can also be directed into reactor 16 fromfeed source 37 through conduit 51. Conduit 51 discharges the feed abovevitreous layer 50. Alternatively, conduit 51 can extend within moltenmetal bath 44 for discharging the feed at a point beneath the surface ofmolten metal bath 44. The feed is suitable for chemical reaction inmolten metal bath 44 to form atomic constituents and at least oneintermediate component. In one embodiment, at least one of the atomicconstituents formed from the feed is exothermally reactive with acomponent of molten metal bath 44. For example, the atomic constituentscan be reactive with the oxidant introduced to molten metal bath 44through tuyere 28.

A portion of the oxidant directed into molten metal bath 44 can alsoreact with atomic carbon and other reactive components to form carbonmonoxide and carbon dioxide, which are substantially stable at theoperating conditions of system 10. Introduction of oxidant into moltenmetal bath 44 can also cause at least a portion of the intermediatecomponent in molten metal bath 44 to exothermically react with theoxidant to form an oxide. Typically, the stoichiometric ratio of oxidantintroduced to system 10 to the oxidizable portion of exothermallyreactive components in molten metal bath 44 is greater than about 1:1.

The coolant, such as a suitable shroud gas, is suitable for cooling theregion within reactor 16 proximate to tuyere 28 under the operatingconditions of system 10. Examples of suitable coolants include nitrogengas (N₂), steam, methane (CH₄), chlorobenzene (C₆ H₅ Cl), etc. In oneembodiment, chlorobenzene is converted by exposure to molten metal bath44 to form hydrocarbon-fragment radicals and chlorine radicals.

Gaseous layer 56 is formed over vitreous layer 50. A reaction zonewithin system 10 includes molten metal bath 44, vitreous layer 50 andgaseous layer 56. Reactants, such as feed and an oxidant, can beintroduced anywhere within the reaction zone. Gaseous layer 56 includesoff-gas formed in molten metal bath 44 and in vitreous layer 50. Off-gasis formed by oxidation of carbonaceous gas and includes reactionproducts, such as hydrogen, water vapor, carbon monoxide and carbondioxide. The off-gas also includes at least one intermediate componentwhich has been entrained or which has been volatilized beforedecomposition to its atomic constituents within molten metal bath 44. Itis to be understood, however, that the conditions of gaseous layer 56can be suitable for forming at least one intermediate component ingaseous layer 56.

In one embodiment, gaseous layer 56 includes an oxidant, such as oxygen,directed into upper portion 14 from oxidant source 26 through secondoxidant inlet tube 57. Atomic constituents formed in molten metal bath44 and in vitreous layer 50 react with oxidant in gaseous layer 56 orwith other materials, such as organic or inorganic compounds, passingthrough gaseous layer 56. Carbonaceous gases formed within molten metalbath 44, such as carbon monoxide and carbon dioxide, are displaced frommolten metal bath 44 as gaseous bubbles. Introduction of oxidant toreactor 12 through second oxidant inlet tube 57 is conducted at a ratesufficient to maintain an oxidant partial pressure in molten metalreactor 12 which allows a substantial portion of atomic carbon in moltenmetal bath 44 to be oxidized.

A substantial portion of the reaction within reactor 12 occurs withinthe reaction zone. Exothermic reaction of atomic constituents formedfrom the feed, such as formation of carbon monoxide and carbon dioxideby reaction of atomic carbon with oxidant, and other exothermicreactions which form inorganic compounds, such as calcium fluoride,generate heat for chemical reaction of the feed and components thereofin the reaction zone.

Heat released by exothermic reaction in the reaction zone can also betransferred out of system 10. In one embodiment, heat is conducted fromlower portion 16 to coil 58. Coil 58 is covered by insulation 60, andcontains a suitable heat transfer medium, such as water or liquid metal.The heat transfer medium is circulated through coil 58 to therebytransfer heat from molten metal bath 44 to power generating means 62. Anexample of a suitable power generating means is a steam turbine.

Off-gas formed in reactor 12 is conducted from the reaction zone throughoff-gas outlet 22 to recirculating fluidized bed reactor 63. Examples ofsuitable recirculating fluidized bed reactors include those which arecommercially available from A. Ahlstrom Corporation, Varkaus, Finland.Recirculating fluidized bed reactor 63 includes reaction vessel 64having vessel inlets 66,68,70 and vessel outlet 72. Cooling jacket 74 isdisposed at vessel inlet 66 for cooling off-gas directed from off-gasoutlet 22 through vessel inlet 66 into reaction vessel 64. A suitablecooling medium is directed from cooling medium source 71 through line 73to jacket 74. Examples of suitable cooling media include, for example,water, ethylene glycol, ethyl benzene, alcohols, etc. Cooling column 76extends from vessel outlet 70 and includes jackets 78,80,82 which areconnected by lines 84,86. Off-gas directed through reaction vessel 64 isdischarged from reaction vessel 64 through vessel outlet 72 and isconducted through cooling column 76 to conduit 88 which is connected tocooling column 76. The off-gas is cooled in cooling column 76 bydirecting cooling medium from cooling medium source 73 through lines84,86,90 and jackets 78,80,82. The off-gas is then discharged fromcooling column 76 and is conducted through conduit 88 to a particleseparator, such as cyclone 92.

Particulates in the off-gas at conduit 88, which have either beencarried as particulates from the reaction zone through reaction vessel64 and cooling column 76, or have formed as condensate in eitherreaction vessel 64 or cooling column 76, are substantially separatedfrom the gas of the off-gas composition in cyclone 92. The gaseouscomponent of the off-gas composition is directed through gaseous outlet94 of cyclone 92 as a gaseous stream.

The gaseous stream discharged through gaseous outlet 94 can be collectedor directed through line 96 for further treatment. Particulates,including dissociation products formed in the reaction zone, aredirected through particulates outlet 98 of cyclone 92 and conductedthrough coolant section 100. The particulates are then carried as aparticulate stream through cooling section 100. The particulate streamis cooled in cooling section 100 by cooling medium directed from coolingmedium source 71. The cooling medium is directed through line, 102 andjacket 104 of cooling section 100. In one embodiment, the particulatestream is cooled to a temperature in the range of between about 100° C.and 300° C. in cooling section 100. At least a portion of theparticulate stream is then conducted from cooling section 100 throughconduit 106 to reaction vessel 64 for mixing with additional off-gascomposition directed from off-gas conduit into reaction vessel 64.

Return of the particulates of the off-gas by recirculating a theparticulate stream causes accumulation of particulates in recirculatingfluidized bed reactor 63. The particulate stream thereby forms a fluidbed of particulates in reaction vessel 64. Generally, the portion of theparticulate stream which is directed from cooling section 100 throughconduit 106 to reaction vessel 64 is in the range of between about fiftyand one-hundred percent of the total volume of the particulate streampassing through cooling section 100.

In addition to particles which are discharged from reactor 12 throughoff-gas conduit 22, or which form within the recirculating fluid bed,other particulates can be added to the recirculating fluid bed fromparticulate source 108. Examples of suitable particulates includeadditional dissociation products or other suitable particulates, suchas, for example, silica, calcium oxide, etc. The additional particulatesare directed from particulate source 108 into hopper 110 and from hopper110 through valve 112 into make-up vessel 114. The particulates are thendirected from make-up vessel 114 through valve 116 in conduit 118through inlet 70 into reaction vessel 64. An inert gas, such as argon ornitrogen can be employed to assist direction of the additionalparticulates to reaction vessel 64.

The cooled particulates of the particulate stream are directed intoreaction vessel 64 and cool the off-gas directed into reaction vessel 64from off-gas conduit 22. In one embodiment, the off-gas in reactionvessel 64 is cooled from a temperature in the range of between about1,000° and 1,500° C. to a temperature in the range of between about 700°and 1,000° C. Volatilized components of the off-gas stream, such asmetal oxides, can condense in reaction vessel 64 and cause agglomerationof particulates in the off-gas and in the fluidized particulate streamdirected into reaction vessel 64. In addition, chemical reactions canoccur in reaction vessel 64. Examples of such chemical reactions includereaction of calcium oxide (CaO), which can be a component of therecirculating fluidized bed, with chlorine gas, which is discharged asan off-gas component from reactor 12. The reaction product is calciumchloride, which precipitates to become a component of the recirculatingfluidized bed. In another example, chemical reactions of components inthe off-gas are kinetically controlled in reaction vessel 64 because theoff-gas is rapidly cooled in reaction vessel 64 by combination of theportion of the particulate stream, which is recirculated to reactionvessel 64. An example of a reaction which is kinetically controlled isformation of ethylene in reaction vessel 64 from methane that isdischarged as an off-gas component from molten metal bath 44 in reactor12. Also, thermodynamically favored reaction off-gas components, can besuppressed by rapid cooling of the off-gas in a kinetically-controlledreaction regime in reaction vessel 64.

The fluid bed and the off-gas combine in reaction vessel 64 and areconducted from reaction vessel 64 through cooling column 76 whereadditional cooling and condensation of volatilized components of theoff-gas continue. Agglomeration of particulates in the combined off-gasand fluidized bed streams can also be caused by continued cooling of thecombined streams as they pass through cooling column 76. The resultingcooled mixture is carried from cooling column 76 through conduit 88 tocyclone 92 for additional separation of the gaseous component of theoff-gas from particulates. The particulates accumulate and are directedfrom cyclone 92 through cooling section 100.

In one embodiment, a second portion of the particulate stream which isconducted through cooling section 100 is discharged from recirculatingfluidized bed reactor 63 through lines 120,122 by pneumatic transportmeans 124. The second portion of the particulate stream can then bereturned to the reaction zone in reactor 12 through tuyere 28.Optionally, at least part of the second portion can be directed to thereaction zone in reactor 12 from line 122 by pneumatic transport means126 through lines 128 and line 51. The dissociation products of theparticulate stream can include intermediates which can be furtherdissociated in the reaction zone to form other dissociation products.Alternatively, the dissociation products can react with components ofadditional waste which is directed into the reaction zone.

Subsequent reactions of the dissociation products which are returned tothe reaction zone can be exothermic or endothermic. For example,partially dissociated organics can condense in recirculating fluidizedbed reactor 63 and, upon return to the reaction zone in reactor 12, canfurther dissociate by endothermic dissociation of its components to formits atomic constituents in molten metal bath 44. Other particulates,such as metal-containing compounds, including metal oxides, can react inan endothermic or exothermic manner in the reaction zone.

In embodiments wherein the returned particulate stream has a netendothermic or exothermic effect, the rate of reaction, such as the rateof dissociation of waste directed into reactor 12, can be controlled bycontrolling the relative amounts of the particulate stream which isreturned to the reaction zone. For example, if the net effect ofreaction of the particulate stream returned to the reaction zone isexothermic, the temperature of the reaction zone and, thus, the rate ofdissociation of waste directed into the reaction zone can be increasedby increasing the portion of the particulate stream which is directedinto the reaction zone. If the net reaction of the particulate stream inthe reaction zone is endothermic, the temperature of the reaction zone,and consequently, the rate of decomposition of waste directed into thereaction zone can be slowed by reducing the rate at which particulatesare directed from recirculating fluidized bed reactor 63 to the reactionzone in reactor 12.

In one very specific example, a dust-laden waste gas is directed fromreactor 12 to the recirculating fluid bed. The gaseous component of thedust-laden waste gas has a nominal composition of about 50% carbonmonoxide gas and 50% hydrogen gas by volume. The normal gas flow ratesof the waste gas is in the range of between about 3 and 5 Nm³ /min. andis at a temperature in the range of between about 1,400° and 1,650° C.The pressure is in the range of between about 0.5 and 2 atmospheres,absolute. The temperature of gas exiting separation section at outlet isabout 300° C. Loading of the recirculating fluidized bed reactor 63 at agas flow rate of 4 Nm³ /min. is about 50gm/Nm³. Distribution of particlesize in the waste gas discharged from the reactor is as follows:90%<40μ; 45% <10μ; 15%<5μ; 4%<2μ and 2%<1μ. The composition of theparticulates in the waste gas is as follows: 84% Fe; 8% CaO; 4% SiO₂ ;2% MgO; and 2% Al₂ O₃. Vitreous forming materials which have a diameterof less than about one millimeter can be used to supplement the fluidbed. Examples of suitable vitreous materials include, for example,calcium oxide and magnesium oxide. Other components of the waste gas caninclude, for example, hydrochloric acid, calcium chloride, zinc, leadand chromium oxide.

Optionally, at least a portion of the second particulate stream can bedirected from conduit 120 through line 122 and line 130 by pneumatictransport means 132 to reactor 134. Reactor 134 has molten bath 136disposed therein. In one embodiment, molten bath 136 includes at leastone molten metal phase suitable for allowing chemical reaction of theintermediate component, such as conversion of the intermediate componentto its atomic constituents and subsequent oxidation of the atomicconstituents, at the operating conditions of system 10. Examples ofsuitable metals of the molten metal phase include metals which aresuitable for forming molten metal bath 44. In one embodiment, moltenbath 136 includes the same composition as molten metal bath 44 and has atemperature sufficient to chemically react at least a portion of theintermediate component, whereby at least a portion of the intermediatecomponent is converted to atomic constituents and subsequently at leasta portion of the atomic constituents react with a component of moltenbath 136, thereby controlling chemical reaction of the feed. Thereaction between the atomic constituents and the component of moltenbath 136 can be exothermic or endothermic.

The second particulate stream is directed into reactor 134 by a suitablemethod and means, such as by the methods and means which are suitablefor directing the second particulate stream into reactor 12. Typically,the second particulate stream is injected into molten bath 136 through atuyere, not shown. An oxidant is directed from oxidant source 26 throughline 138 and a tuyere, not shown, into molten bath 136. Coolant isdirected from coolant source 34 through line 140 for injection intomolten bath 136, with waste and oxidant, through their respectivetuyeres. The off-gas generated in reactor 136 is directed throughoff-gas conduit 142 to inlet 66 of reaction vessel 64.

As can be seen in FIG. 2, the gaseous stream is conducted through line96 to second recirculating fluid bed 144. Second recirculating fluidizedbed reactor 144 is substantially the same as recirculating fluidized bedreactor 63 shown in FIG. 1 and includes reaction vessel 146, coolingcolumn 148, separation section 150, cyclone 152 and recirculation line154. A fluid bed is formed in second recirculating fluidized bed reactor144 by, for example, directing a suitable particulate from particulatesource 156 through conduit 158 to reaction vessel 146. Residualparticulates in the gaseous stream which enters reaction vessel 146through line 96 can combine with the recirculating fluidized bed and,thus, separate from the gaseous stream in separation section 150.Selectivity for enhancement of kinetically-controlled reactions andsuppression of thermodynamically-favored reaction can be controlled bycontrolling the make-up, temperature, pressure, and rate of therecirculation.

Also, volatilized components in the gaseous stream can condense insecond recirculating fluidized bed reactor 144 and be separated from thegaseous stream to become a component of the fluid bed. At least aportion of the fluid bed is recirculated to reaction vessel 146 throughrecirculation line 154. Optionally, a second portion of the fluid bed isdischarged from recirculating fluidized bed reactor 144 through line160. The second portion of the fluid bed can then be directed, bypneumatic transport means, not shown, to reaction vessel 68, reactor 12or reactor 136 for additional processing. The second portion of thefluid bed can be collected for processing or purification of componentsin the bed by suitable means, not shown.

The gaseous stream discharged from separation section 150 is conductedthrough line 162 to filtration section 164. In one embodiment,filtration section 164 includes a high-efficiency particle adsorber-typefilter (HEPA filter) and a carbon filter. Alternatively, filtrationsection 164 can include a ceramic porous plug. Examples of componentswhich can be removed from the gaseous stream include volatilized heavymetals which can physico-chemically absorb or adsorb onto the particlesof the fluid bed. Also, particles which are not separated from the fluidbed can be removed from the gaseous stream in filtration section 164.From filtration section 164, the gaseous stream is directed through line166 and seal tank 168, to the atmosphere through vent 170. Optionally,the gaseous stream can be directed from seal tank 168 through line 172to thermal oxidizer 174 for combustion of any remaining oxidizablecomponent of the gaseous stream and before discharge to the atmospherethrough vent 176.

Equivalents

Those skilled in the art will recognize, or be able to ascertain usingno more than routine experimentation, many equivalents of the inventiondescribed specifically herein. Such equivalents are intended to beencompassed in the scope of the following claims.

I claim:
 1. An apparatus for treating a gaseous discharge stream formedfrom a waste in a molten metal bath, comprising:a) a reactor having amolten metal bath formed therein and a gaseous discharge port above themolten metal bath; b) a reaction section extending from the gaseousdischarge port; c) a cooling column extending from the reaction section;d) separation means in fluid communication with the cooling section forseparating a particulate dissociation product from a gaseous componentof a gaseous discharge stream formed from a waste in the reactor andpassing from the reactor through the reaction section and the coolingcolumn into said separation means; e) a gaseous discharge conduitextending from the separation means; f) a cooling section extending fromthe separation means for cooling a particulate stream formed of theparticulate dissociation product separated from the gaseous dischargestream in said separation means; g) a recirculation conduit extendingfrom the cooling section to the reaction section for conducting at leastportion of the particulate stream from the cooling section to thereaction section; and h) a recycle conduit extending from the coolingsection to the reactor for recycling a portion of the particulate streamfrom the cooling section to the reactor for submerged injection into themolten metal bath.
 2. An apparatus for claim 1 further including asecond reactor and means for conducting a portion of the particulatestream from the cooling section to a second molten metal bath formed insaid second reactor.
 3. An apparatus of claim 2 further includingmake-up means connected to the reaction section for directing aparticulate into the reaction section as the gaseous discharge streampasses through the reaction section, whereby a particulate bed can beformed in the reaction section and in the cooling column.
 4. Anapparatus of claim 3 further including a filter connected to the gaseousdischarge conduit for separating a residual particulate component fromthe gaseous discharge stream.
 5. An apparatus of claim 4 wherein thefilter includes a porous plug.
 6. An apparatus of claim 5 wherein theporous plug is formed of a ceramic material.
 7. An apparatus of claim 4wherein the filter includes an adsorbent.
 8. An apparatus of claim 1wherein the separation means includes a cyclone.
 9. An apparatus fortreating a gaseous discharge stream formed from a waste in a moltenmetal bath, comprising:a) a reactor containing a molten metal bath, thereactor including means for directing a waste into the reactor, whereina gaseous discharge stream is formed from the waste, and means fordischarging the gaseous discharge stream from the reactor; b) arecirculating fluidized bed reactor for treating the gaseous dischargestream; c) means for directing the gaseous discharge stream from thereactor to the recirculating fluidized bed reactor; and d) recyclingmeans extending from the recirculating fluidized bed reactor forrecycling a portion of a particulate stream from the recirculatingfluidized bed reactor to the reactor containing the molten metal bathfor submerged injection into the molten metal bath.